Partly decoupled tree-ring width and leaf phenology response to 20th century temperature change in Sweden

The recent warming trend, and associated shifts in growing season length, challenge the principle of uniformitarianism, i.e., that current relations are persistent over time, complicates uncritical inferences past climate from tree-ring data. Here we conduct a comparison between width chronologies Pinus sylvestris L. (Scots pine), Picea abies (L.) Karst. (Norway spruce) Betula pubescens Ehrh. (Downy birch) phenological observations (budburst leaf senescence) Fagus sylvatica (European beech), Quercus robur oak), sp. (Birch), Norway spruce Scots pine) Sweden to assess what extent width–temperature relationship timing phases affected by increased temperature. Daily meteorological confirm prolongation thermal season, most consistently observed as an earlier onset around 1–2 weeks since beginning 20th century. Observations budburst closely mimic this pattern, with deciduous trees occurring 1–2.5 earlier. In contrast changes seen phenology observational temperature data, relationships remain surprisingly stable throughout spruce, pine Downy birch all show significant correlations at least one 30 day-long window starting late June–early July season. displays largest degree stability, consistent 60 correlation Julian calendar day 150. Thus, our results suggest uniformitarianism is not violated during period covered modern observations. Further research needed determine thresholds sensitivity these species may alter or deteriorate consequence ongoing change.